1. Field of the Invention
The present invention relates to an optical scanning apparatus and more particularly to a transmissive and reflective optical scanning apparatus.
2. Description of the Related Art
Recent developments in the use of high speed, low cost digital electronic imaging systems to process, transmit and display digital information have substantially increased the demand for optical scanners to convert information into a digital electronic form. A variety of optical scanners, including facsimile machines and digital copiers, have been developed to meet this growing demand. The optical scanners generally fall within two categories, reflective scanners for opaque objects, such as documents and photographs, and transmissive scanners for transparent objects, such as slides and transparencies. Reflective scanners, used with opaque objects, project light onto the side of the object to be scanned. The object illuminated by the reflected light is then viewed by a digital camera which converts the image into a digital electronic form. Transmissive scanners, used with transparent objects, project light through the object to be scanned. The transmissive object is also viewed by a digital camera to then be stored in a digital electronic form. The growing demand for both reflective and transmissive scanners has resulted in a need for scanners to provide both capabilities.
Present dual scanner designs, as illustrated in FIG. 7, utilize a conventional reflective base scanner 20. This type of scanner includes a digital camera and a reflective light source (not shown) mounted on rails and driven by a motor within the base housing to scan along the length of the document. The light source projects light upon the portion of the object within the field of view of the camera. Documents and photographs are placed on a glass platen 22. The light source and camera move incrementally lengthwise across a document under the glass platen to scan in an image line by line. This conventional reflective scanner design has been modified with the addition of a second light source 24 for transmissive objects. This light is preferably housed behind a second glass platen 26 within a lid 28 which overlies the base 20. The light source 24 is movably mounted on a pair of rails and wired electronically to the reflective scanner base to provide light through a portion of a transmissive object within the field of view of the camera. The transmissive light source mechanism includes a motor 28 to maintain the light directly within the camera's field of view by incrementally moving along the rails in the lid in synchronous movement with the camera.
In order to obtain the best picture quality from the design presently used.,the light source located in the lid must be maintained in synchronous alignment with the camera at all times during scanning. The electronic communication between the lid light source and the scanner base is necessary to maintain synchronous movement. Thus in addition to a second drive mechanism such a scanner requires additional electronic circuitry in both the scanner and the scanner lid to maintain the light 24 in alignment with the camera. This adds additional cost to the manufacture of the device.
Furthermore, the glass platen 22 located on the scanner base 20 must include physical properties to eliminate distortion from the reflective light source below the base glass platen as well as the transmissive light source within the lid. This problem is unique to the dual transmissive and reflective scanner, because ordinary transmissive scanners do not include a glass plate in between the image and the scanner; rather they are designed to position the object to be scanned directly within the field of view of the camera to improve the image quality. The improved image quality is important to transmissive scanners, because there is a great demand for high resolution graphics reproduction.
As described above, the conventional transmissive and reflective scanners are unable to provide an unobstructed path for the transmissive scanning of objects. They also require more moving parts and increased electronic circuiting which leads to a higher manufacturing cost. Thus, the need exists for a transmissive and reflective scanner which is low in cost easy to manufacture and provides an unobstructed pathway for developing high quality transmissive images as well as including a reflective scanning capability.